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The Plants of Vacant Lots
Nature Bulletin No. 391-A October 17, 1970
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
THE PLANTS OF VACANT LOTS
If all vacant lots could be turned into well-tended gardens or smooth
grassy playgrounds, it would be a fine thing. However, in cities and
town, their topsoil has been either removed or so disturbed and abused
by digging and filling that little will grow except the toughest of plants -
- weeds, that thrive on neglect. Because these weeds are the same ones
that make us so much work and trouble around our homes, gardens and
farms, we hate them.
A weed is merely a plant growing where it is not wanted. Weeds have
bold aggressive plant personalities, each kind with striking, easily
recognized features. Where there are weeds there is also a host of
insects and other small animal life such as slugs, snails, pillbugs,
centipedes and worms. Native birds and small mammals, too, find food
and shelter there. In fact, a weedy vacant lot offers unusual
opportunities for interesting studies in nature. One can be found within
five minutes walk of almost any school in metropolitan Chicago. They
should be used to add life to science courses which too often depend
too much on dried plants, dried insects, and drier books.
After the wreckage had been cleared away following the air raids over
London in 1940 and 1941, there were a number of news stories about
botanists finding plants growing there which had not been seen near
London for over a century. The same sort of thing happens in our forest
preserves when we plow strips to stop the spread of fire. These fire
lanes do not grow up in the kinds of plants native to our woodlands and
prairies but with the common weeds of farms and gardens.
These plants which come into newly broken or cultivated soil are, with
a few exceptions such as the ragweeds, all foreign plants. The seeds of
most of them were brought to this country in colonial times -- mixed
with garden seeds, in cattle feed, in packing materials, or as stowaways.
Most of them arrived in America free of their natural enemies in the
Old World and found few native plants equipped to offer much
competition to their rapid spread in cultivated soil. They spread
westward with the early settlers. In Illinois, sandburs popped up along
the Sangamon River in the 1830's. By 1852, black mustard, sheperd's
purse, purslane, wild parsnip, mullein, hemp and several foreign grasses
were growing near Peoria. Each decade has seen the arrival of others.
Weeds produce large numbers of seeds, usually quite small, often lying
dormant for many years. Counts of the average numbers of seeds from a
single full-grown plant give such figures as: dandelion, 1792;
cocklebur, 9700; ragweed, 23,100; purslane, 69,000; pigweed, 85,000;
crabgrass, 89,600; and foxtail, 113,600.
Different weeds scatter their seeds in different ways. Those of
milkweeds and thistles are airborne; velvet-leaf and pigweed seeds drift
with snow or slide over ice; old-witch grass and Russian thistle are
tumbleweeds; the giant ragweed, bindweed and smartweed seeds are
carried by water; birds carry the berries of nightshade, the seed pods of
pepper grass and, in mud on their feet, almost any kind. Burdock,
cocklebur, and dozens more, cling to the coats of animals; but the long
distance travelers ride with man himself.
A weed has also been defined as a plant for which we have discovered
no use, and certainly some of them seem unpromising. Too many are
either stringy, bitter, smelly, prickly, fuzzy, poisonous, or give us hay
fever. On the credit side, many have gay flowers, some make fine salad
greens, and a few yield useful drugs.
Best
of all, they give first aid to injured soil and prevent erosion.
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Update: June 2012
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